Crystal furnace

ABSTRACT

A chamber is provided which includes baffles, plates, and support members situated around a centrally located heater and crucible to define a hot zone in the lower half of the chamber where gas currents are quickly heated and thence sent to the upper half of the chamber. As a result, the motion of these currents around the hot zone is reduced, which reduction permits thermal gradients to be maintained around the crucible for controlling crystal growth therein. A resistance heater provides heat for a crystal melt contained inside the crucible.

-l l Jan. 14, 1975 United States Patent [191 Ford [ CRYSTAL FURNACE Primary ExaminerR. N. Envall Jr. 1 t.wll M.F dPl Al'[,Clf.

nven or 1 mm or a O 0 an Attorney, Agent, or Firm-A. C. Smith T C A R T S B A H 5 [22] Filed: 1973 A chamber is provided which includes baffles, plates,

and support members situated around a centrally located heater and crucible to define a hot zone in the 211 Appl. No.: 410,852

lower half of the chamber where gas currents are quickly heated and thence sent to the upper half of the chamber. As a result, the motion of these currents around the hot zone is reduced, which reduction permits thermal gradients to be maintained around the 145 303 M 3 l1 N75 22 3F .0 .2 u 3 H l m h C r u a H e u S l. m l 5mm UIF lll 2 8 555 lll [56] References Cited UNITED STATES PATENTS crucible for controlling crystal growth therein. A resistance heater provides heat for a crystal melt contained inside the crucible.

13/31 2 Claims, 1 Drawing Figure 2.640,86l 6/1953 Kremers.....1............................ 3.409.730 11/1968 Ehihara...... 3414661 12/1968 Reed v 22 29M U33 [9 29 CRYSTAL FURNACE BACKGROUND OF THE INVENTION Certain crystal growing chambers known in the prior art employ radio-frequency induction coils for heating a crystal melt. These chambers require large coolingcoil systems to dissipate the heat produced by the induction coils. Chambers of this type also produce high speed gas currents which conduct heat away from a crucible where the crystal melt is heated. Attempts to control these gas currents have been hindered by the cooling-coil system, and, as a result, it has been impossible to maintain vertical and horizontal thermal gradients around the crucible, which gradients are essential to produce crystals of low dislocation density and low strain.

BRIEF SUMMARY OF THE INVENTION According to a preferred embodiment of the invention a plurality of baffles, plates, and supporting members for thebaffles are disposed around a crucible and a heater for defining a hot zone around these two elements. The baffles are tubular and are located at a short distance away from the heater. The support members support the baffles on the internal chamber walls. One plate covers the top of the baffles and is provided with an opening through which the crucible may pass and another is located below the baffles and serves as a heat shield. Gas currents ascending or descending within the chamber must pass through the abovementioned hot zone and thence they are sent to the upper part of the chamber. As a result the gas currents within the chamber are reduced and thermal gradients can be maintained around the crucible to aid in controlling the growth of a crystal in the crucible.

According to the invention the heater used in the preferred embodiment is a resistance heater whose walls are formed by vertically undulated segments of rectangular design. By using this type of heater it is possible to produce a great deal of heat around the crucible and to have the space to install heatprotecting and directing baffles for conserving heat around the crucible and for controlling the gas currents inside the chamber.

DESCRIPTION OF THE DRAWING FIG. 1 shows a side view of the furnace.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a chamber including an upper half 13 and a lower half 15. Water-cooled flanges 17 and 19 join together halves l3 and 15. A flange 21 located at the upper end of half 13 and a flange 23 located at the lower end of half are the means by which the chamber 10 is attached to a support assembly (not shown). Water-cooling pipes 25 are disposed in spiraling design on the outer walls of chamber 10. These walls and the water-cooling pipes 25 are coated with copper to provide uniform heat flow and dissipation outside chamber 10.

A support flange 27 attached to flange 23 includes a plurality of openings 22. Electrodes 29, a thermocouple connector (not shown), and a susceptor support 33 pass through openings 22 which are fitted to maintain a pressure level inside chamber 10. Electrodes 29 bring power for a heater 41, the thermocouple connector transmits a signal representing the temperature around a crucible 39, and susceptor support 33 supports a susceptor 37. Susceptor 37 contains crucible 39 wherein a crystal melt is heated by heater 41. This heater surrounds susceptor 37 and is made of materials which are stable at the melting temperatures of the crystal materials, for instance, gallium phosphide. The walls of heater 41 are formed by a continuous series of undulating or square segments vertically oriented and extending from the bottom to the top of the walls. However, other heater designs could be equally effective, for instance helical designs. The heater walls are much longer than those of crucible 39 and produce a continuous range of thermal gradients along their length. Thus crucible 39 can be moved inside heater 41 to a point where a crystal melt inside crucible 39 receives a required amount of heat. This point can be changed to meet the changing heat needs of the melt during a crystal growing process. For this purpose, susceptor 37 and crucible 39 can be rotated and moved up and down by rotating and sliding susceptor support 33 within the opening 22 of support flange 27.

Baffles 43 and 45 made of low-thermal conductivity materials surround heater 41 to conserve heat around curcible 39. An insulator baffle 44 is placed between baffles 43 and 45. Support members 47 and 49 support baffles 43 and 45, respectively, and join these baffles to the internal walls 20 of chamber 10. A heat shield plate 51 is located below heater 41 and is affixed to the internal walls of chamber 10. This plate has a number of openings through which electrodes 22, susceptor support 33, and a thermocouple connector (not shown) pass. An internal plate 53 situated above heater 41 is attached to the top ends of baffles 43 and 45. This plate extends from wall to wall inside the chamber and has an opening through which susceptor 37 may pass. Support members 47 and 49, baffles 43 and 45, and plates 51 and 53 define a hot zone around heater 41 and crucible 39, which zone is located away from the cold walls of chamber 10. Initially, cold chamber gases pass through this hot zone where they are heated and thence sent to the upper half 13 of chamber 10. When the gases in the upper half 13 cool off and tend to go to the lower part of the chamber, they must pass through the hot zone for all other paths are blocked off by internal plate 53 and support members 47 and 49. As those gases enter the hot zone, they are quickly heated within a short distance from the entrance and sent back up to the upper half 13 of chamber 10. This control over chamber gases prevents the circulation of convection gas currents around the hot zone and permits thermal gradients to be set up and maintained around crucible 39 for controlling crystal growth.

Viewing ports 55 and 57 situated on the chamber upper half 13 are disposed to permit unobstructed viewing of the mouth of the crucible 39. These ports may include hollow extensions 56 having an outer lens 50 and an inner lens 52.en These lenses are made of a suitable material, such as quartz, to withstand the high operating temperatures occurring inside chamber 10.

A plate 9 attached to flange 21 includes an opening having a seal for conserving a pressure level inside chamber 10. A rod 62 slides and turns within the opening. Rod 62 is used to introduce a crystal seed into or lift a crystal from a crystal melt located in crucible 39.

I claim:

1. A crystal growing furnace, comprising:

3 4 a chamber having internal walls and external walls; heat-conserving zone around the heater and below acrucible disposed inside the chamber for containing said plate and for establishing an upper region a crystal melt; above said plate, said internal plate having an means supporting said crucible for selectively moving opening through which the crucible may pass into said crucible inside said chamber; 5 and above the heat-conserving zone. a resistance heater surrounding the crucible; 2. A crystal growing furnace as in claim 1 wherein the baffle means surrounding the heater and crucible for chamber includes an upper plate having an opening conserving heat; therein, and a rod entering the chamber through said an internal plate within the chamber in cooperating opening for placing a crystal seed in the crucible.

disposition with the baffle means for defining a 

1. A crystal growing furnace, comprising: a chamber having internal walls and external walls; a crucible disposed inside the chamber for containing a crystal melt; means supporting said crucible for selectively moving said crucible inside said chamber; a resistance heater surrounding the crucible; baffle means surrounding the heater and crucible for conserving heat; an internal plate within the chamber in cooperating disposition with the baffle means for defining a Heat-conserving zone around the heater and below said plate and for establishing an upper region above said plate, said internal plate having an opening through which the crucible may pass into and above the heat-conserving zone.
 2. A crystal growing furnace as in claim 1 wherein the chamber includes an upper plate having an opening therein, and a rod entering the chamber through said opening for placing a crystal seed in the crucible. 